JP2905304B2 - Activation determination device for air-fuel ratio sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an activation determination device for an air-fuel ratio sensor which can accurately detect an active point of the air-fuel ratio sensor without deteriorating an air-fuel ratio sensor for detecting an air-fuel ratio of an engine. .

[0002]

2. Description of the Related Art In recent years, in order to accurately control the air-fuel ratio of the intake air-fuel mixture of an internal combustion engine to a target value over the entire range of the used air-fuel ratio, an exhaust gas system is provided with a full-range air-fuel ratio sensor to correlate with the air-fuel ratio. It has been proposed that the exhaust gas component to be detected is detected and the fuel supply amount is feedback-controlled.

[0003] Such an air-fuel ratio sensor does not function unless the temperature of the element section becomes higher than about 400 to 500 ° C. Therefore, a heater for heating the sensor element section is provided, and the sensor element section is heated to an activation temperature or higher. Although a heater is provided to maintain the sensor, the sensor may be damaged if the sensor element temperature is not higher than the activation temperature after starting the heater, such as when the engine is started from a low sensor temperature. There is a possibility that.

Various methods for determining the activation of the air-fuel ratio sensor have been proposed.
As described in JP-A-61-241652,
A method for determining that activation of a sensor has been completed when a predetermined time has elapsed after application of a heater to a sensor, and a method disclosed in Japanese Patent Application Laid-Open No. 64-9357.
As described in Japanese Patent Application Laid-Open Publication No. H11-264, there is known a method of determining an active state when the voltage between the electrodes of a battery element and a pump element is within a predetermined range in a state where a current flows to a pump element of a sensor. This conventional example will be described below with reference to the drawings.

FIG. 8 is a block diagram of a conventional engine control system for performing air-fuel ratio control using an air-fuel ratio sensor. FIG.
FIG. 9 is a configuration diagram of an embodiment of an air-fuel ratio control apparatus according to the present invention, which will be described later, and FIG. 9 is a time chart at the time of sensor startup for explaining a conventional sensor startup method. Hereinafter, the conventional apparatus will be described with reference to FIGS. 8 and 9 (a conventional time chart at the time of starting the sensor), and will be described with reference to FIG. 1 as necessary.

In FIG. 8, reference numeral 1 denotes an air-fuel ratio sensor,
2 is a sensor control amplifier of the air-fuel ratio sensor 1, 3 is an engine rotation sensor, 4 is an intake air amount sensor, 5 is a cooling water temperature sensor of the engine 30, 6 is a fuel injection valve, 7 is an air-fuel ratio control device, 8 is a throttle valve, 9 is a throttle opening sensor of the throttle valve 8, and 32 is an intake pipe.

In FIG. 8, an engine rotation sensor 3
Detects the engine speed Ne, the intake air amount sensor 4 detects the intake air amount Qe, the throttle opening degree sensor 8 detects the throttle opening degree θ, the cooling water temperature sensor 5 detects the cooling water temperature WT, and these detections are performed. Values are output to the air-fuel ratio control device 7, and these detected values are
Is a state quantity indicating the operating state of the vehicle.

The air-fuel ratio of the air-fuel mixture of the intake air introduced through the throttle valve 8 and the fuel injected from the fuel injection valve 6 in the intake pipe 32 is determined by the air-fuel ratio sensor 1 attached to the exhaust pipe 31. The air-fuel ratio output is similarly detected by the sensor control amplifier 2 and sent to the air-fuel ratio control device 7 by the sensor control amplifier 2.

Next, a detailed configuration of the air-fuel ratio sensor 1 will be described with reference to FIG. In FIG. 1, an air-fuel ratio sensor 1
Is composed of a sensor element section 11 and a heater 12. The sensor element section 11 includes an oxygen pump element 11a, an oxygen concentration cell element 11
b, a diffusion chamber 11c, and an atmosphere chamber 11d. The sensor control amplifier 2 includes a differential integration amplifier 21 as a pump current control unit, a differential amplifier 22 and a non-inverting amplifier 23 as a pump current detection unit, and a pump voltage detection unit. , A cut transistor 25 as a pump current cutting means, and a heater control circuit 26.

The voltage of the oxygen concentration cell element 11b is connected to the inverting input terminal of the differential integrating amplifier 21, the reference voltage Vref is connected to the non-inverting input terminal, and the output of the differential integrating amplifier 21 is detected by the oxygen pump element 11a. Input through a resistor Rs,
The voltage across the current detection resistor Rs is input to the non-inverting input terminal and the inverting input terminal of the differential amplifier 22, the output terminal of the non-inverting amplifier 23 is connected to the inverting input terminal, and the output of the differential amplifier 22 is non-inverting. The offset voltage V _OB is connected to the non-inverting input terminal of the amplifier 23, the inverting input terminal is connected to the offset voltage V _OB , the non-inverting input terminal of the non-inverting input terminal is the applied voltage of the oxygen pump element 11a, and the inverting input terminal is the offset voltage VPB. Is connected.

Next, the configuration of the air-fuel ratio control device 7 will be described. The air-fuel ratio control device 7 includes a multiplexer 71
a, 71b, analog / digital (hereinafter, referred to as A / D) converters 72a, 72b, an input interface (hereinafter, referred to as I / F) 73, and a microprocessor (hereinafter, μ-P).
74, a read-only memory (hereinafter referred to as ROM) 75, a random access memory (hereinafter referred to as RAM).
76), output I / Fs 77a and 77b, and a fuel injection valve driving circuit 78. The output Ne of the engine rotation sensor 3 is supplied via the input I / F 73 to the output Qa of the intake air amount sensor 4 and the cooling water temperature sensor 5 respectively. Is output from the multiplexer 71b via the A / D converter 72b to the μ-P
74, the non-inverting amplifier 2 of the sensor control amplifier 2
3 and the outputs V _O and V _{PO of the} non-inverting amplifier 24 are similarly output from the multiplexer 71a via the A / D converter 72a.
-P74, and the fuel injection valve 6 is connected to the fuel injection valve drive circuit 78 and controlled via the output I / F 77b.
The cut transistor 2 of the sensor control amplifier 2
5. The heater control circuit 26 is controlled via the output I / F 77a.

Next, the operation of this conventional example will be described.
The engine 30 is operated and the heater 12 of the air-fuel ratio sensor 1 is turned on.
Is driven and controlled by the heater control circuit 26, and the sensor element 1
In the state where 1 is activated, the oxygen concentration cell element 11b
An electromotive force Vs corresponding to the oxygen concentration difference between the diffusion chamber 11c and the atmosphere chamber 11d is generated.

The sensor electromotive force Vs is supplied to a predetermined reference voltage Vref via a differential integrating amplifier 21 and a current detection resistor Rs.
When the pump current I _P is supplied to the oxygen pump element 11a so as to control the pump current I _P , the pump current I _P is proportional to the air-fuel ratio.

Therefore, the pump current I _P is supplied to the detection resistor R
s, amplified by the differential amplifier 22, and
At 3, the offset voltage V _OB is given to obtain the air-fuel ratio output V _O. Here, the offset voltage V _OB is the pump current I _P is the direction differs rich zone of the air-fuel ratio (rich) and lean region (lean), regardless of the direction of the pump current I _P, the air-fuel ratio output V _O Is set to a positive output.

The air-fuel ratio control device 7 has a ROM 75
Based on the program and data stored in the
e, the intake air amount Qa, the throttle opening θ, the cooling water temperature WT, and the like, to calculate a target air-fuel ratio by μ-P74, and to calculate the target air-fuel ratio and the actual air-fuel ratio converted from the measured air-fuel ratio output V _O. Based on the deviation, the valve opening time of the fuel injection valve 6 is corrected, and fuel corresponding to the valve opening time is injected from the fuel injection valve 6 so that the air-fuel ratio of the engine 30 becomes the target air-fuel ratio. I do. The RAM 76 is used for temporarily storing data at this time.

FIG. 9 is a time chart when the air-fuel ratio sensor 1 is started. Here, a case where the air-fuel ratio is rich after the engine is started will be described as an example. The heater 12 of the air-fuel ratio sensor 1 starts heating according to a drive command given to the heater control circuit 26 from the μ-P 74 via the output I / F 77a at the same time as the start of the engine 30.

At this time, in a region where the temperature Ts of the sensor element section 11 is about 400 ° C. or less, the electromotive force Vs of the oxygen concentration cell element 11b remains low.
Has a large input deviation, and therefore a large pump voltage _VP is applied to the pump element 11a.

The pump voltage output V _PO is _supplied to the non-inverting amplifier 2
Offset voltage V _PB is positive output which is added to the pump voltage V _P at 4. At this time, since the impedance of the pump element 11a is high, the pump current I _P hardly flows, and the air-fuel ratio output V _O becomes almost the offset voltage V _OB .

When the temperature Ts approaches about 400 to 500 ° C., the electromotive force Vs of the oxygen concentration cell element 11b rises to about the reference voltage Vref. At this time, the constant control is performed with the reference voltage Vref of the sensor electromotive force Vs. established to the pump voltage V _P is the direction of supplying oxygen to the diffusion chamber 11c, i.e., in the direction the pump voltage output V _PO is V _PO ≦ V _PB,
Pump current I _P is gradually converged to a current value indicating the air-fuel ratio at that time, the temperature Ts is complete convergence at about 700 ° C..

Therefore, in order to detect the above-mentioned activation point, conventionally, as shown in the figure, an activation judgment for judging activation when the pump voltage output V _PO falls within a predetermined allowable voltage range V _PB ± ΔV _PB. A method and a means for detecting the sensor electromotive force Vs are further provided so that the difference ΔVs between the sensor electromotive force Vs and the reference voltage Vref is within a certain range and the pump voltage output V _PO is within a predetermined allowable voltage range V _PB ± ΔV _PB An activation determination method such as determining that the sensor is activated when it is within the range has been proposed.

[0021]

However, in such a conventional activation judging method, the sensor element 1
Since a large voltage is continuously applied to the pump element 11a in a state where the temperature of the sensor 1 is low, deterioration of the sensor is promoted and durability of the sensor is deteriorated. To solve this problem, a timer is provided after the start of the air-fuel ratio sensor. During this timer period, the cut transistor 25 is turned on so that the pump current does not flow through the oxygen pump element 11a. A method has been proposed in which a pump current is supplied to the oxygen pump element 11a by turning off the pump 25.

However, since the timer period cannot be an index of the sensor characteristics, if the operating state changes after starting and the temperature rise of the sensor element section 11 decreases, the timer period ends. The sensor element unit 11 may not be activated, or may be conversely restarted after running.
If the temperature rises quickly, the timer period may not end even though the air-fuel ratio sensor 1 has already been activated, making it difficult to determine the active point accurately. Was.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and can accurately detect an activation point of an air-fuel ratio sensor without deteriorating the air-fuel ratio sensor. An object of the present invention is to provide an activation determination device for an air-fuel ratio sensor that can perform the same activation determination even when the sensor enters the inactive region again after activation.

[0024]

According to the present invention, there is provided an air-fuel ratio sensor having an air-fuel ratio sensor comprising an oxygen concentration cell element and an oxygen pump element and a heater for heating the oxygen concentration cell element and the oxygen pump element. Pump current control means for controlling a pump current flowing through the oxygen pump element so that the electromotive force of the oxygen concentration cell element becomes a predetermined reference voltage, and a pump current controlled by the pump current control means is detected. Pump current detecting means, pump current cutting means for stopping supply of the pump current, positive voltage detecting means for detecting a pump voltage applied to the oxygen pump element, heater power supply means for supplying power to the heater, , serial pump voltage allowable range having different corresponding to each target air-fuel ratio of the pump current or the engine is stored in advance Means, with at the pump current cut state from the heater power supply means to start supplying power to the heater, and a timer means for releasing a predetermined time pump current cut every predetermined period from the start time of this supply, the timer Pump current based on the setting time of the means
Measure the pump voltage by causing the control means to perform pump current control
The pump voltage is stored in the previously stored pump.
When the voltage is within the allowable range, the air-fuel ratio sensor is activated.
State and the pump current cut
An air-fuel ratio control device for canceling the state is provided.

[0025]

According to the present invention, the supply of electric power to the heater is started from the heater power supply means in the pump current cut state, and the pump current cut is canceled for a predetermined time by the timer means for a predetermined time from the start time, so that the pump current is reduced. The pump current is controlled by the control means, the pump current flowing through the oxygen pump element at this time is measured by the pump current detection means, and when the pump voltage falls within the pump voltage allowable range stored in advance, the pump current becomes empty. It is determined that the fuel ratio sensor is in the active state, and the pump current cut state is released.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an air-fuel ratio sensor activation judging device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention, which is the same as the configuration of the above-mentioned conventional example. Although the description of the configuration here is omitted, the activation determination procedure of the air-fuel ratio sensor in the apparatus of the present invention is shown. Is different from the conventional one.

FIG. 2 is a flow chart for explaining a procedure for determining the activation of the air-fuel ratio sensor by the apparatus of the present invention. FIG. 5 is a view showing a pre-stored allowable pump voltage range with respect to the air-fuel ratio output. FIG. 7 is a time chart at the time of activation of the air-fuel ratio sensor when the activation determination is performed according to the present invention.

First, when the engine 30 shown in FIG. 8 is started, it is determined by the μ-P 74 of the air-fuel ratio control device 7 in step 101 of FIG.
If it is in the start mode, the output I / F 7 is
The cut-off transistor 25 of the sensor control amplifier 2 is turned on via the switch 7a, the potential of the oxygen pump element 11a is grounded, and the pump current cut (I
_P cut), and the output I /
The heater control circuit 26 is activated via F77a, power is supplied to the heater 12, and heating of the sensor element unit 11 is started.

Next, at step 104, as shown in FIG. 7, a timer is started and a predetermined time t1 is set.
When the time t1 ends in step 105, the cut transistor 25 is turned off in step 106, and the oxygen pump element 11a controls the differential integrating amplifier 21 so that the electromotive force of the oxygen concentration cell element 11b matches the reference voltage Vref. An output voltage is applied, and this voltage causes the pump current I _P
Flows.

Next, in step 107, step 1
With the release of the pump cut at 06, as shown in FIG.
The time t0 is set, and the pump cut release is continued during the time t0. During this time, at step 108, the air-fuel ratio output V _O and the pump voltage V corresponding to the pump current I _P are set.
_A multiplexer 71 outputs a pump voltage output V _PO corresponding to _P.
The signal is A / D converted by the A / D converter 72a via a, and is read into the μ-P 74.

The duration of the time t0 depends on the response of the sensor and the PI constant of the differential integrating amplifier 21.
The time period may be as short as about sec and about 1 to 5% shorter than the time t1.

When the time t0 ends in the next step 109, the air-fuel ratio output V _O and the pump voltage output V _PO immediately before the end of the time t0.
At step 110, the pump voltage output allowable range map shown in FIG. 6 stored in advance in the ROM 75 is read out, and the pump voltage output V _PO enters the V _PO allowable range corresponding to the air-fuel ratio output V _O. Step 1
It is determined at 11.

If the result of this determination is that the pump is out of the allowable range, pump cut is performed again in step 102, and the processing procedure from step 104 to step 111 is repeated. It is determined that the fuel ratio sensor is activated, and the process proceeds to the next process.

As shown in FIG. 5, the pump current when the sensor electromotive force Vs is controlled to be constant at the reference voltage Vref,
That is, the lower the sensor element temperature Ts, the larger the deviation of the pump voltage with respect to the air-fuel ratio output V _O , that is, the pump voltage output V _PO , from the offset voltage V _PB , and the electromotive force Vs is constantly controlled to the reference voltage Vref. If not, the output V _PO becomes the maximum output regardless of the air-fuel ratio.

Therefore, by setting the allowable range of the pump voltage output to a region surrounded by oblique lines in the figure, the activation temperature of the sensor element can be accurately determined.

FIG. 7 is a time chart showing the activation judgment at the time of starting the engine in the above embodiment.
0, the heater 12 is driven, and the timer shows the state of the air-fuel ratio output V _O and the pump voltage output V _PO when the pump cut is released for the time t0 at the interval of the time t1. -Fuel ratio output V _O
, The allowable range of the pump voltage output with respect to is indicated by the shaded area, and in the figure, the pump voltage output V _PO is within the allowable range at the fifth timer, the activation is determined, and the pump cut is released. I have.

In particular, although not shown, the element temperature Ts at the time of this activation determination is about 500 ° C., as is apparent from comparison with FIG. 9 showing a state at the time of startup according to the conventional method.

That is, according to the above embodiment, when the sensor element temperature is low such that the sensor electromotive force constant control cannot be established, the voltage is applied to the oxygen pump element 11a only for a very short period of time t0. There is an advantage that the air-fuel ratio sensor 11 is not deteriorated or damaged due to the activation determination processing. Further, since the allowable range of the pump voltage output which is determined to be active based on the sensor output V _O is changed, there is an advantage that the activation can be accurately determined regardless of the starting air-fuel ratio.

Next, a second embodiment of the present invention will be described. FIG. 3 is a flowchart showing the procedure for determining the activation of the air-fuel ratio sensor according to the second embodiment, and FIG.
FIG. 8 is a diagram showing an allowable pump voltage range with respect to a target air-fuel ratio stored in advance in the example of FIG.

In FIG. 3, steps 101 and 10
2 is the same as steps 101 and 102 in FIG. 2 described above. When the heater control is started in step 103, the cooling water temperature WT is detected by the cooling water temperature sensor 5 in step 112, and the cooling water temperature WT is detected via the multiplexer 71b. / D converter 7
A / D conversion is performed in 2b, and the data is read into μ-P74.

Next, at step 113, the value of the time t1 is given and determined as a decreasing function t1 (WT) with respect to the cooling water temperature WT.
1 (WT) is set.

Here, as in the case of restarting the engine in a short time after traveling, the temperature of the exhaust pipe 31 (FIG. 8) to which the air-fuel ratio sensor 1 is attached is relatively high, and the exhaust gas temperature rises quickly. In this case, the activation of the sensor element is fast, but in this case, if the cooling water temperature WT is high, the period of the time t1 is shortened, so that there is an advantage that the activation determination is not delayed by the timer.

Next, when the time t1 ends in step 105, the time t0 is set in step 107 along with the release of the pump cut in step 106.
At 08, the sensor output V _O and the pump voltage output V _PO are read, and at step 114, the engine speed Ne, the intake air amount Qa, and the cooling water temperature WT indicating the operating state of the engine are read. At step 115, the engine speed Ne, A target air-fuel ratio AFO corresponding to the intake air amount Qa and the cooling water temperature WT is calculated.

Next, when time t0 ends in step 109, the target air-fuel ratio AFO shown in FIG. 6 is used in step 116 using the target air-fuel ratio AFO immediately before the end of time t0.
The allowable pump voltage range stored in advance for RO
M75 is read out, and it is determined in step 111 whether or not it is within the allowable range. If it is within the allowable range, activation is determined. Therefore, the same effect as in the above embodiment can be obtained in the second embodiment.

[0045] In the above embodiments, the air-fuel ratio output V _O is used at the time of determination, the air-fuel ratio output V _O which is repeatedly measured in the time t0 period in the pump voltage output V _PO, pump voltage output V
_{Of the PO} , the value immediately before the end of the time t0 is used, but the duration of the time t0 is determined by the air-fuel ratio output V as described above.
_O, previously determined by considering the response of the pump voltage output V _PO
Therefore, the air-fuel ratio output V _O and the pump voltage output V _PO measured only once immediately before the end of the time t0 may be used.

Next, a third embodiment of the present invention will be described. FIG. 4 is a flowchart showing an activation determination procedure according to the third embodiment. After an activation determination is made using time t1 and the pump current cut state is released, time t2 is set in step 117. Similarly, during the time t2, the air-fuel ratio output V _O and the pump voltage output V _PO are read in step 109, and
From 0 to 111, it is determined whether or not the pump voltage output V _PO is within the allowable pump voltage range.

When the pump voltage output V _PO deviates from the allowable pump voltage range, the pump current is cut and the time t1 is reset. When the pump voltage output V _PO is within the allowable pump voltage range, the time t2 is set at step 118. Only when is completed, in step 119, the target air-fuel ratio control using the air-fuel ratio output V _O is performed.

That is, in the case of the third embodiment,
After the activation at the sensor element temperature of about 500 ° C. is determined using the time t1, while waiting until the sensor temperature reaches about 700 ° C. at which the air-fuel ratio output V _O is stabilized, the weighting is performed at the time t2. There is an advantage that even when the sensor element temperature decreases due to a change in state of the engine or the like during the period and the sensor becomes inactive, it can be clearly detected.

Although the embodiment shown in FIG. 4 shows the case where the period of the time t2 is fixed, as shown in FIG. 2, the period of the time t2 may be a decreasing function of the cooling water temperature TW.
Also, whether the pump voltage output V _PO is within the allowable pump voltage range is determined in the same manner as shown in FIG.
May be used.

[0050]

As described above, according to the present invention, the supply of power from the heater power supply means to the heater in the pump current cut state is started, and the timer means sets the start time to a predetermined time every predetermined period from the start time. The pump current cut is canceled, the pump current is controlled, and the pump voltage is measured.If the pump voltage falls within the pump voltage allowable range stored in advance, it is determined that the air-fuel ratio sensor is in the active state. Since the determination is made and the pump current cut state is released, the air-fuel ratio sensor is not deteriorated or damaged due to the activation determination process, and the activation determination is performed accurately regardless of the starting air-fuel ratio. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 shows the activity of an air-fuel ratio sensor according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a conversion determination device .

FIG. 2 is a flowchart showing an activation measurement procedure according to a first embodiment of the activation determination device for an air-fuel ratio sensor of the present invention.

FIG. 3 is a flowchart showing an activation measurement procedure by an activation determination device for an air-fuel ratio sensor according to a second embodiment of the present invention;

FIG. 4 is a flowchart showing an activation determination procedure of an air-fuel ratio sensor activation determination device according to a third embodiment of the present invention;

FIG. 5 is an explanatory diagram showing an allowable pump voltage range with respect to an air-fuel ratio output in the activation determination device for an air-fuel ratio sensor of the present invention.

FIG. 6 is an explanatory diagram showing an allowable pump voltage range with respect to a target air-fuel ratio in the activation determination device for an air-fuel ratio sensor of the present invention.

FIG. 7 is a time chart at the time of activation of the sensor according to the activation procedure in the activation determination apparatus for the air-fuel ratio sensor of the present invention.

FIG. 8 is a configuration diagram of an engine control system applied to a conventional method for determining activation of an air-fuel ratio sensor.

FIG. 9 is a time chart at the time of activation of a sensor applied to a conventional method for determining activation of an air-fuel ratio sensor.

[Explanation of symbols]

Reference Signs List 1 air-fuel ratio sensor 11a oxygen pump element 11b oxygen concentration cell element 11c diffusion chamber 12 heater 2 sensor control amplifier 21 differential integration amplifier 22 differential amplifier 23, 24 non-inverting amplifier 25 cut transistor 26 heater control circuit 7 air-fuel ratio control device 72a , 72b A / D converter 74 Microprocessor 75 ROM 77a, 77b Output I / F

Claims (1)

(57) [Claims] 1. An oxygen concentration cell element comprising an oxygen ion-conductive solid electrolyte material provided in an exhaust system of an engine and having electrodes attached thereto and arranged across a diffusion chamber into which exhaust gas of the engine is diffused and introduced. An air-fuel ratio sensor comprising an oxygen pump element, a heater for heating the oxygen concentration cell element and the oxygen pump element, and a pump current flowing through the oxygen pump element so that the electromotive force of the oxygen concentration cell element becomes a predetermined reference voltage. , A pump current detecting means for detecting a pump current controlled by the pump current controlling means, a pump current cutting means for stopping the supply of the pump current, and a voltage applied to the oxygen pump element. Posop voltage detection means for detecting a pump voltage, heater power supply means for supplying power to the heater, and each of the pump current or the engine Storage means for storing in advance a pump voltage allowable range that has been varied according to the target air-fuel ratio;
Timer means for starting supply of power to the heater from the heater power supply means in a pump current cut state, and for canceling the pump current cut for a predetermined time every predetermined period from the start time of the supply, and setting of the timer means The pump current control means performs pump current control based on time and measures a pump voltage.If the pump voltage falls within the previously stored pump voltage allowable range, the air-fuel ratio sensor is activated. An activation determination device for an air-fuel ratio sensor, comprising: an air-fuel ratio control device that determines that there is a pump current and cancels the pump current cut state.